The invention relates to a pressure-reducing valve according to the preamble of claim 1.
Such pressure-reducing valves make available at their secondary pressure connections a generally adjustable secondary or working pressure which can be used by connected compressed-air consumers. The pressure-reducing valve provides a constant working pressure irrespective of fluctuations in the primary pressure or in the consumption of compressed air by the compressed-air consumers.
DE-U-296 18 080 discloses a pressure regulator comprising a primary duct which, in operation, guides a pressure medium which is under a primary pressure, a secondary duct which is provided in order to guide a pressure medium which is under a secondary pressure, a control valve which is provided in the connection between the primary duct and the secondary duct and which has a valve member which is used to influence the passage cross-section available to the pressure medium, and a control chamber which can be acted upon by the secondary pressure and which is delimited by a movable wall, the outside of which, remote from the control chamber, is acted upon by an adjusting spring and the inside of which, facing the control chamber, cooperates with the valve member. The primary duct, the secondary duct and the control chamber of the pressure regulator, which chamber is formed separately from the secondary duct, are connected to an electrically operated control valve device which can be switched over between a working position, in which it produces a connection between the control chamber and the secondary duct, and a closing position in which it produces a connection between the control chamber and the primary duct.
The known pressure regulator is very complicated in terms of its structure and also requires an external electrically operated control valve device.
A structurally substantially more compact pressure-reducing valve which can additionally be in the form of a functional screw fitting, is known from EP-B-0 086 902. It has the following components:
a valve housing which has a primary pressure connection and a secondary pressure connection,
a first connecting duct provided in the valve housing between the primary pressure connection and the secondary pressure connection,
a slide which is movable to and fro in the valve housing between an opening and a closing position of the first connecting duct,
an operating element which forces the slide into the opening position by means of a spring,
seals which are provided between the valve housing and the slide and by means of which a first pressure chamber is formed at one end region of the slide, a second pressure chamber is formed in the central region of the slide and a third pressure chamber is formed at the other end region, the first and second pressure chambers being connected to one another in the opening position of the slide by way of the first connecting duct,
a second connecting duct formed in the slide and connecting the first and third pressure chambers to one another,
and a fourth pressure chamber which is provided in the region of the operating element and which is in operative connection with the secondary pressure connection by way of a third connecting duct provided in the valve housing, the secondary pressure prevailing in the fourth pressure chamber acting on the operating element against the force of the spring.
That known pressure-reducing valve has a primary pressure relief, as a result of which the spring forcing the slide into the opening position can be correspondingly smaller and more compact.
On the basis of that prior art, the problem of the invention is to provide a pressure-reducing valve according to the preamble of claim 1 which has secondary pressure relief and which is distinguished by a simple and compact structure.
According to the invention, the problem is solved by the features of claim 1.
Further forms of the invention are the subject-matter of the subsidiary claims.
In the pressure-reducing valve according to the invention, the second pressure chamber in the central region of the slide is exposed to the primary pressure via the primary pressure connection. The first and third pressure chambers at the end regions of the slide are, on the other hand, exposed to the secondary pressure via the secondary pressure connection. In addition, the third and fourth pressure chambers are connected to one another by way of the third connecting duct.
In a preferred embodiment, a second spring is also provided which forces the slide in the direction towards the operating element. In addition, the seal provided between the first and second pressure chambers cooperates with a valve seat.
In a special embodiment, a ventilation opening is provided in the fourth pressure chamber and is arranged in the contact region between the operating element and the slide.
In order to set the set pressure, in a preferred embodiment an adjusting device is provided for setting the preloading of the first spring, the slide being moved from the opening position into the closing position when the secondary pressure prevailing in the fourth pressure chamber exceeds the set pressure.
The form according to the invention also requires only three seals which are provided between the first and second pressure chambers, between the second and third pressure chambers and for sealing the fourth pressure chamber. The third seal provided for sealing the fourth pressure chamber may be in the form of, for example, a moulded seal.
The pressure-reducing valve according to the invention may also be in the form of a functional screw fitting.
Further advantages and forms of the invention will be explained in detail by means of the following description of an embodiment and the drawings.